1. Field of the Invention
The present invention relates generally to the use of polyfunctional (cyclic imido)-1,3,5-triazine compounds as crosslinking agents in curable compositions, and particularly powder coating compositions, as well as the preparation of novel prepolymers of such polyfunctional (cyclic imido)-1,3,5-triazine compounds which may also find use as crosslinking agents in curable compositions. The present invention also relates to certain of these polyfunctional (cyclic imido)-1,3,5-triazine compounds which in and of themselves are novel, as well as methods of preparing polyfunctional (cyclic imido)-1,3,5-triazines in general.
2. Description of Related Art
Various derivatives of amino compounds, such as amino-1,3,5-triazines and glycolurils, are described in the literature for use in a wide variety of fields. Certain of these derivatives, such as the partially or fully alkoxymethylated derivatives of melamine, guanamines and glycoluril, are useful as crosslinkers in curable compositions which contain resins having active hydrogen groups. See, for example, U.S. Pat. No. 4,064,191, U.S. Pat. No. 4,081,426, U.S. Pat. No. 4,101,520, U.S. Pat. No. 4,118,437, U.S. Pat. No. 4,129,681, U.S. Pat. No. 4,243,705, U.S. Pat. No. 4,271,277, U.S. Pat. No. 4,276,212, U.S. Pat. No. 4,330,458, U.S. Pat. No. 4,374,164, U.S. Pat. No. 4,433,143, U.S. Pat. No. 4,425,466, U.S. Pat. No. 4,873,298, U.S. Pat. No. 5,155,201, U.S. Pat. No. 5,256,713 and WO96/41826.
While these derivatives in general provide excellent results, they may release volatiles (including formaldehyde) during cure which is not desired. Thus, crosslinking agents with good performance characteristics and which minimize the release of volatiles during cure would be particularly advantageous and are highly desired.
One non-formaldehyde emitting alternative is the class of isocyanate and carbamate functional 1,3,5-triazine crosslinking agents disclosed in U.S. Pat. No. 4,939,213, U.S. Pat. No. 5,084,541, U.S. Pat. No. 5,288,865, EP-A-0604922, EP-A-0624577, EP-A-0649842, WO95/30663, WO96/04258, WO96/11915, WO96/15185, and U.S. application Ser. No. 60/002,950 (filed Aug. 30, 1995). Other non-formaldehyde emitting alternatives include, for example, the class of lactam substituted 1,3,5-triazine crosslinking agents disclosed in WO93/10117, and the class of acetal and enamine functional 1,3,5-triazine cross-linking agents disclosed in WO96/29318. The aforementioned have been found to be particularly useful as crosslinkers in coating compositions based on active hydrogen and/or epoxy groups containing resins, with the cured coatings possessing a wide range of desirable properties.
While some of these alternatives have shown great promise, the search continues for replacements for traditional amino derivative crosslinkers, which replacements retain many of the desirable properties of the traditional crosslinkers but which emit little or no volatiles on cure. As discussed in further detail below, the present inventors have found another such suitable replacement in polyfunctional (cyclic imido)-1,3,5-triazines.
Certain narrow classes of cyclic imido functional 1,3,5-triazines have been disclosed in the art. For example, U.S. Pat. No. 3,794,641 discloses mono- and polyfunctional phthalimido-1,3,5-triazines, which are stated to have herbicidal activity. The phthalimido-1,3,5-triazines are prepared by reacting cyanuric chloride with an alkali-metal phthalimide.
Romanian Patent No. 59672 and 89171 disclose polyfunctional maleimido-1,3,5-triazines, methods of preparing the same and uses thereof. Specifically, Romanian Patent No. 59672 discloses the use of such maleimido functional 1,3,5-triazines in the preparation of polyamine-polyimides by reacting these compounds in solution with aromatic diamines by Michael addition at the maleimide double bond. The resulting polyamine-polyamides are said to be useful in the preparation of fiber-reinforced laminates. Romanian Patent No. 89171 discloses a method of preparing such polyfunctional maleimido-1,3,5-triazines by reacting melamine and maleic anhydride in the presence of cyclohexanone as solvent and further in the presence of diphenylnitrosamine as a polymerization inhibitor.
WO94/13664 discloses mono(tetrahydrophthalo) melamine, which is stated to be a soluble melamine derivative useful as a reactive flame-retardant additive and as an intermediate in the preparation of other reactive flame-retardant additives.
Finally, EP-A-0409334 discloses mono(maleimido), mono(succinimido), mono(phthalimido) and another monofunctional 1,3,5-triazine, which are stated to be useful in the preparation of aromatic polymers with anisotropic behavior.
All of the above-mentioned references are hereby incorporated by reference herein for all purposes as if fully set forth.
None of these references, however, discloses or suggests the use of polyfunctional (cyclic imido)-1,3,5-triazines as crosslinking agents in powder coating compositions, prepolymers of these polyfunctional (cyclic imido)-1,3,5-triazines, the methods of making these compounds nor the various species of polyfunctional (cyclic imido)-1,3,5-triazines, in accordance with the present invention as described in further detail below and as set forth in the present claims.